The Importance and Place of Methemoglobin and Carboxyhemoglobin Levels in the Diagnosis and Prognosis of Pulmonary Embolism.

Background
This is a retrospective study to investigate the effects of Carboxyhemoglobin (COHb) and Methemoglobin (MetHb) levels in the diagnosis and prognosis of Pulmonary Thromboembolism (PTE).


Materials and Methods
Cases that were confirmed with PTE diagnosis using CT Pulmonary Angiography (CTPA) or Ventilation/Perfusion Scintigraphy were accepted as pulmonary embolism. And patients which were excluded using the same methods were accepted as the control group. Patients with carbon monoxide poisoning, Chronic Obstructive Pulmonary Disease (COPD), sepsis, pneumonia, asthma, idiopathic pulmonary fibrosis, bronchiectasis, decompensated cardiac failure or those who used drugs that cause methemoglobinemia (sulphanomides, dapson, phenacetin, primacine, benzocaine) were not included in the study.


Results
In our study, 462 patients were examined with an initial PTE diagnosis. Among these patients, 107 patients who met the inclusion criteria were included in the study. The mean age of all patients was 56.44 ±17.3 years (21-86) and the mean age of patients with PTE diagnosis was 55.3 years and the mean age of excluded patients was 59 years (p:0.27). When the blood gas parameters of both groups were compared, COHb levels in the groups with PTE diagnosis were statistically significantly higher (p=0.001), and the PO2 levels in the group excluded for PTE diagnosis were statistically significantly higher (p=0.028). In our study, six of our patients (8.1%) died in the early stages because of PTE.


Conclusion
In our study, COHb level was found to be statistically significant in the group with PTE. However, this value was not higher than the normal COHb level in the blood. We found that MetHb and COHb levels were not statistically significant in the prognosis of PTE.


INTRODUCTION
Pulmonary Thromboembolism (PTE) can be defined as blocking of the pulmonary artery or one of its branches with materials (thrombus, tumor, air or fat) from another part of the body (1)(2)(3). PTE is a disease that is commonly seen in the chest diseases practice and has a mortality rate of 10-15% within the first three months period after the diagnosis (4,5). There is no single laboratory marker for definite diagnosis of PTE. Therefore, studies are mostly focused on an ideal marker that provides a diagnosis. Ideal prognostic and diagnostic markers should be easily evaluated and tested. Methemoglobin (MetHb) and Carboxyhemoglobin (COHb) are values that can easily be measured in the blood gas.
Increase in HO-1 is a sign of oxidative stress as a general indicator (10).
In order for hemoglobin to bind reversibly with oxygen and carry oxygen to tissues, iron should be kept in ferric (Fe 2+) form. Hemoglobin in Ferric (Fe 3+) form which has oxidized iron atom and is unable to bind oxygen is called MetHb (14)(15)(16)(17). In some medical conditions such as painful attacks that are seen in sepsis, gastrointestinal infections and sickle cell anemia, MetHb could occur due to contact with toxic agents and chemical substances. Hypoxia and oxidative stress are known to increase MetHb formation (15)(16)(17)(18)(19)

Data evaluation
Results were reported as the mean ± SD and categorical variables were given as percentages.

Ethics of the Study
The study was approved by the Ethics Board of School of Medicine of Akdeniz University.

CONCLUSION
Consequently PTE is a frequent disease that could result in mortality. In our study, COHb level was found to be statistically significant in the group with PTE. However, this value was not higher than the normal COHb level in the blood. Different from the only study in the literature, we found that MetHb and COHb levels were not statistically significant in the prognosis of PTE. We think that this difference is caused by the characteristics of the patient population. We believe that, this should be supported with prospective studies.

Author Contributions
Prof. Ozbudak was the supervisor. The other author collected, analyzed and calculated the data. All authors wrote the separate parts of manuscript.

Funding
This research received no external funding.